Zhuojin Pipe Fitting Co., LtdStability Analysis of Super-Large Span CFST Arch Bridge During Construction Under Static Wind Load
Literature Overview
This paper by Zeng Yong and Mo Lei from Chongqing Jiaotong University, published in the Journal of Henan Urban Construction College in 2022 (Vol. 31, No. 3, pp. 1-7), presents a stability analysis of the Hejiang Yangtze River Bridge—a 530-meter mid-rise steel tube concrete (CFST) arch bridge—during its construction phase. The study specifically examines the maximum cantilever stage of arch rib erection, where the last two cross braces have not yet been installed. The research was supported by multiple Chongqing municipal and national research funding programs, reflecting the significance of this engineering challenge.
Engineering Background and Problem Definition
The Hejiang Yangtze River Bridge represents a significant engineering achievement with its 530-meter main span tower-cable-arch integrated system. During construction, the arch ribs are erected incrementally from both sides toward the crown, creating a temporary cantilevered structure that is particularly vulnerable to stability issues before the arch is closed and cross bracing is completed.
The maximum cantilever stage—where the last two cross braces remain uninstalled—represents the most critical phase for structural stability. At this stage:
- The arch rib acts as a cantilever beam with minimal lateral restraint
- The tower-cable-arch system is partially formed, with incomplete load paths
- Wind loads acting on the exposed arch rib can induce significant lateral displacement
- Geometric nonlinearities become prominent as the structure deflects under load
Analytical Methodology
Finite Element Modeling
The researchers developed a comprehensive three-dimensional finite element model using ANSYS software that captures the tower-cable-beam integrated structural system. The model accounts for:
- Geometric nonlinearity: Large displacement effects are included to capture the true structural response under significant lateral loads
- Load nonlinearity: The P-delta effect is considered, where axial forces acting through displaced geometry create additional moments
- Cable pretension: The initial tension in the stay cables is accurately modeled to represent the actual construction sequence
- Material properties: Both steel and concrete material properties are defined with appropriate nonlinear constitutive relationships
Analysis Stages
| Analysis Type | Objective | Key Output |
|---|---|---|
| Static analysis | Determine displacements under design wind load | Maximum lateral displacement (1.72 m at crown) |
| Stability analysis | Evaluate structural stability margin | Critical load factor |
| Sensitivity analysis | Identify critical parameters | Influence of cross brace spacing |
Boundary Conditions and Load Cases
The half-span model was analyzed with appropriate boundary conditions representing the actual construction state. The static wind load was applied according to relevant bridge design codes, considering the aerodynamic characteristics of the partially erected arch rib. The wind pressure distribution on the exposed arch rib geometry was carefully defined to reflect the actual cross-sectional shape and orientation.
Key Results and Discussion
Displacement Analysis
The maximum lateral displacement of 1.72 meters occurring at the arch crown represents a significant but acceptable deflection for a 530-meter span structure. This displacement corresponds to approximately 1/308 of the main span, which is within typical serviceability limits for bridge structures. The displacement distribution along the arch rib follows the expected pattern for a cantilever beam, with maximum deflection at the free end (crown) and zero at the fixed end (springing).
Stability Assessment
The stability analysis confirmed that the tower-cable-arch structural system satisfies both displacement and stability requirements during the maximum cantilever stage. The critical load factor exceeds unity, indicating that the structure has adequate stability margin against buckling or instability under the design wind load.
The key finding is that the tower-cable system provides effective lateral restraint to the arch rib, even before the arch is closed. The stay cables act as tension members that restrain lateral movement of the arch rib through their geometric stiffness contribution. This is a critical insight for construction planning, as it confirms that the temporary structure is stable without requiring additional temporary bracing beyond the design cross braces.
Cross Brace Influence
The analysis highlights the importance of the last two cross braces in providing lateral stability to the arch rib. Their absence during the maximum cantilever stage represents the most unfavorable condition, and their timely installation is essential for maintaining structural integrity. The spacing and connection details of these cross braces directly influence the lateral stiffness of the arch rib system.
Engineering Practice Integration
Construction Sequencing Implications
The stability analysis results directly inform construction sequencing decisions. The analysis confirms that:
- The arch rib erection sequence must ensure that cross braces are installed at planned intervals to maintain adequate lateral stability
- Wind load limits must be monitored during the maximum cantilever stage, with work suspension protocols activated when wind speeds exceed design thresholds
- The tower-cable system must be properly tensioned before arch rib erection begins to ensure the lateral restraint mechanism is fully engaged
- Temporary monitoring systems should be installed at critical locations to verify that measured displacements correspond to predicted values
Quality Control Considerations
From a steel pipe manufacturing and welding quality perspective, several factors are critical for ensuring the stability analysis assumptions are valid:
| Quality Parameter | Relevance to Stability | Acceptance Criteria |
|---|---|---|
| Steel tube wall thickness uniformity | Affects bending stiffness | Per GB/T 8163 or API 5L |
| Weld quality at cross brace connections | Critical for load transfer | Full RT/UT inspection |
| Concrete fill quality | Affects composite action | Density and strength verification |
| Steel tube straightness | Influences geometric imperfection | Within tolerance per EN 10219 |
| Connection bolt pretension | Ensures intended structural action | Torque verification |
The stability of the temporary structure depends critically on the quality of the steel tubes and their welded connections. Any deficiency in wall thickness, weld quality, or connection integrity can reduce the actual stiffness below the analyzed values, potentially compromising the stability margin.
Study Insights and Reflections
This research demonstrates the importance of rigorous stability analysis during the construction phase of large-span CFST arch bridges. The construction phase often represents the most vulnerable period for structural integrity, as the structure is incomplete and may have reduced redundancy compared to the final as-built condition.
The methodology presented—combining geometric and load nonlinearities in a comprehensive finite element model—provides a robust analytical framework that can be adapted to other large-span bridge projects. The key insight for engineering practice is that the tower-cable-arch integrated system provides inherent lateral stability through its geometric configuration, even during incomplete construction states. However, this stability is conditional upon proper construction sequencing, timely installation of cross braces, and rigorous quality control of all structural components.
For engineers involved in the design and construction of similar large-span CFST arch bridges, this paper provides valuable guidance on the analytical approach, critical parameters, and quality control measures necessary to ensure structural safety during construction.